From DE-PS 35 39 220 a control and regulating device of this kind is known in which the switching device is connected to both working lines via a single working pressure signal line and a shuttle valve, has three gear positions, one being a blocking middle position, and, when an idling speed of the driving motor is exceeded, is actuated by the control signal through a travel-direction control valve to engage neutral or else forward or reverse gear if one of the latter gears is engaged. By this actuation the switching device is switched into one of the two outer gear positions according to the gear engaged, in order to act on the corresponding side of the displacement-direction control valve with the working pressure signal so that the adjusting device will tilt the hydraulic pump out into the appropriate direction of displacement.
In the absence of the control signal, i.e. at idling speed or with neutral engaged, actuation of the switching device by with the control signal ceases and the switching device is thereupon switched by pressure from a spring into the blocking middle setting in which it interrupts the action of the working pressure signal on the displacement-direction control valve, which is consequently neither actuated by the control signal nor acted on by the working pressure signal. Spring pressure adjusts the valve and thus, via the adjusting device, the hydraulic pump, into the zero setting. After the hydraulic pump has slowed to a standstill the hydraulic pump takes over the support against the effect of the load, which seeks to move under the acceleration of gravity. In practice, however, it has been found that after a fairly short time pressure losses, for example due to unavoidable leakage, occur in the working line carrying the high pressure, so that the hydraulic motor is not adequately supported by the hydraulic pump and consequently begins to rotate if the mechanical brake is not applied; the load can thus not be kept at a standstill in this way. This disadvantage can also occur as a result of other factors, for example, play in the hydraulic pump adjustment which prevents its exact setting to zero displacement volume. Thus under practical operating conditions secure and adequate support of the load cannot be guaranteed without the use of the mechanical brake. Furthermore it is not possible to accelerate the load against the acceleration due to gravity while maintaining the neutral setting. This procedure, which is here called "shunting", is particularly important for example in parking when the transmission is used in motor vehicles or for correcting the position of the load when the transmission is used in lifting devices.